The third generation partnership project (3GPP) and 3GPP2 are currently considering long term evolution (LTE) of the universal mobile telecommunication system (UMTS) terrestrial radio access (UTRA). Currently, single carrier frequency division multiple access (SC-FDMA) and orthogonal frequency division multiple access (OFDMA) are being considered for uplink and downlink air interface for the evolved UTRA (E-UTRA).
In SC-FDMA and OFDMA, a plurality of orthogonal subcarriers are divided into a plurality of subcarrier blocks, (also known as “resource blocks” (RBs)). An RB is a basic scheduling unit for uplink transmissions in an SC-FDMA system. Depending on a data rate or a buffer status, at least one RB or resource block group (RBG) is assigned for a wireless transmit/receive unit (WTRU) for uplink and downlink transmission.
Multiple-input multiple-output (MIMO) refers to the type of wireless transmission and reception scheme where both a transmitter and a receiver employ more than one antenna. A MIMO system takes advantage of the spatial diversity or spatial multiplexing to improve the signal-to-noise ratio (SNR) and increases throughput. Multi-user MIMO (MU-MIMO) is the scheme that more than one user data is allocated to the antennas or spatial streams, while single-user MIMO (SU-MIMO) is the scheme that only one user data is transmitted via multiple antennas or spatial streams.
Downlink scheduling grant control signaling is essential to a MIMO system for both SU-MIMO and MU-MIMO because efficient downlink scheduling grant control signaling may improve MIMO link performance, system capacity and spectrum efficiency.